For example, in manufacturing a semiconductor device, processes such as a film forming process, an oxidation process, a diffusion process, an annealing process, and an etching process are performed on a semiconductor wafer, which is an object to be processed. When such processes are performed, a vertical heat treatment device, which is provided with a process vessel in which an object to be processed is accommodated and a heater unit disposed in an outer peripheral side of the process vessel to surround the process vessel, is used.
The heater unit of the vertical heat treatment device is configured to include, for example, a resistive heating element (heater element) and a circular cylindrical thermal insulation wall body installed around the heater element. Specifically, a holding unit configured to accommodate the heater element into the holding unit is installed in an inner peripheral side of the thermal insulation wall body, and the heater element is disposed in a spiral shape by the holding unit.
Here, the thermal insulation wall body in the vertical heat treatment device is formed by stacking a plurality of ring-shaped thermal insulation blocks having the holding unit in an axial direction. In addition, there is disclosed a thermal insulation wall body which is formed by dispersing a material of the thermal insulation wall body in an aqueous medium into a slurry phase, bringing the slurry into contact with a forming mold having a surface corresponding to the shape of the holding unit, and drying the slurry.
However, in the method of stacking a plurality of ring-shaped thermal insulation blocks in the axial direction, a long period of time and tremendous efforts are needed to manufacture the thermal insulation wall body. Further, in the above-described method of manufacturing the thermal insulation wall body, there are problems in that special equipment is required and it is difficult to form the holding unit having a depth sufficient to hold the heater element.